At sacrifice, Hri−/− and Hri+/+ littermate mice appeared overall healthy, although we noted that all the knockout mice had developed splenomegaly (Fig. 5A), a characteristic that has been reported previously (32, 33) in Hri−/− mice and relates to a progressive anemia and defective erythropoiesis in these mice. This evidence concerns the gene EIF2AK1 and anemia.